Polyamide resins composed of xylylenediamine and C.sub.6 -C.sub.20 .alpha.,.omega.-linear aliphatic dibasic acids (hereinafter will be referred to as "MX nylon") possess excellent chemical resistance, tensile strength and modulus of elasticity, but have low impact strength and are apt to cause brittle fracture at normal temperatures. Due to this defect little industrial value has been found in use of MX nylon alone.
Again polyamides such as polyamide-6, polyamide-66 and the like are short of impact strength if used by themselves, and various proposals have been made to improve that property.
On the other hand, as a means for improving impact strength of these polyamide resins, a resin obtained by simply blending MX nylon with above polyamide, especially a blend resin prepared by melting and kneading these polyamide resins at the extrusion temperature conditions employed in an ordinary molding machine, was made the subject of a patent application (U.S. patent application Ser. No. 525,598).
However, MX nylon and polyamide-6 are essentially scanty of compatibility with each other, and it is impossible to obtain molded articles of high mechanical strength from such simple blends.
Attempts to blend a specific elastomer with a polyamide resin have also been made.
British Patent 998,439 discloses a thermoplastic resin composition composed of 50-99% by weight of a linear polyamide and 50-1% by weight of an olefin copolymer particles, said olefin copolymer containing 0.1-10 mol % of an acid group(s).
U.S. Pat. No. 3,845,163 shows a resin composition which is an ionic copolymer formed by blending a polyamide with an .alpha.-olefin/.alpha.,.beta.-ethylenically unsaturated carboxylic acid copolymer with the view to improve toughness of the molded articles, at least 10% of the acid group of said .alpha.,.beta.-ethylenically unsaturated carboxylic acid being neutralized with a metallic ion(s).
The compositions disclosed in these patents, however, are still insufficient as to impact strength. Thus heretofore no attempts to improve the impact strength were made to blend MX nylon, which especially has low hygroscopicity and exhibits excellent dimensional stability after molding, with other polyamide resin to form a polymer alloy.
The main object of the present invention therefore resides in the provision of a polyamide resin for molding, which is free of above-described defects and exhibits excellent performance in impact resistance, mechanical strength, dimensional stability, chemical resistance and processability, and also in the provision of a polyamide resin composition formed by blending the polyamide resin with an elastomer.